1. Field of the Present Invention
The present invention relates to a barrel type susceptor for use in an epitaxial growth, and more particularly to a barrel type susceptor in which inclination angles of a bottom surface of a wafer mounting concave portion is changed with positions in a height direction.
2. Description of the Related Art
Generally, an epitaxial apparatus is used for manufacturing an epitaxial wafer. As the epitaxial apparatus, a barrel type susceptor is mostly employed.
A conventional barrel type susceptor 61 has a susceptor main body 62 having a shape of a hollow polygonal truncated cone (e.g., pentagonal, hexagonal, heptagonal and tetragonal truncated cone), a polygonal top plate 63 provided on a top of the susceptor main body 62 so as to suspend the susceptor main body 62, and an polygonal bottom plate 64 provided on the bottom to shield a gas flow, as shown in FIG. 8.
The susceptor main body 62 is made of a carbon member coated with SiC, and cut out of special carbon structural material, or formed in its configuration by integrally attaching eight high trapezoidal face plates to a top plate and a bottom plate. On each planar face plates 65 of the susceptor main body 62, a plurality of wafer mounting concave portions 66a for mounting a semiconductor wafer W are aligned in a longitudinal direction. Also, a bottom face 66a1 of the wafer mounting concave portion 66a is provided at a constant inclination angle θd of 0° to 5° to the vertical axis.
When an epitaxial wafer is produced, employing this conventional barrel type susceptor and an epitaxial apparatus 70 as shown in FIG. 9, a wafer Wa on the uppermost stage of the susceptor and a wafer Wc on the lowermost stage have a greater film thickness, and a wafer Wb on the middle stage has a smaller film thickness. Accordingly, a uniform film thickness distribution was not obtained within the wafer and batch. The film thickness distribution is controlled by changing a temperature distribution in the epitaxial growth. However, even though the uniform film thickness is obtained by changing the temperature distribution, at the same time, the uniformity of the resistivity is made worse. Therefore, the temperature distribution cannot be changed.
Moreover, as a method for improving the uniformity of the film thickness distribution while keeping the temperature distribution uniform from the uppermost stage of the susceptor to the lowermost stage, there is a method of changing a flow rate of a source gas. This is the method in which the flow rate near a gas introduction portion is changed by shifting a position of a gas introduction nozzle upwardly or downwardly. However, this method can apply in a case that the thickness on the uppermost stage or the lowermost stage is thick. In this case, the uniformity of the film thickness distribution is improved. The film thickness distribution obtained by this method is shown in FIG. 7, in which there is a limited dispersion with the conventional barrel type susceptor. When adopting this method, for producing high quality productions, a method for decreasing the dispersion within the batch by reducing the number of stages for mounting the wafer is adopted. Accordingly, productivity is lower in the conventional method.
Referring to Japanese Patent Unexamined Publication no. JP-A-6-151339, paragraphs 0014, 0015 and 0018, and FIG. 1, a barrel type susceptor has been proposed which has the susceptor main body and removable wafer arranging parts. In the proposed susceptor, the angle of a reaction gas acting on the wafer is changed in accordance with the wafer arranging parts having appropriately different shapes at the time of an epitaxial growth process or every time of the process to improve the crystalline of the epitaxial layer and the uniformity of film thickness. However, in the proposed susceptor, since the wafer arranging parts are changed at the time of the epitaxial growth process or every time of the process, it takes a lot of time to change the parts and the mounting of wafers, resulting in lower productivity.